The present invention relates to single piston, cam driven high pressure fuel pumps for generating high pressure fuel in common rail direct injection gasoline engines.
It is known in the industry that the pump must incorporate an outlet check valve to prevent pressure bleed back from the rail while the pump is in the intake stroke cycle. It has become an industry requirement to incorporate a pressure relief valve within the pump to protect the entire high pressure system from an unexpected excess pressure caused by a system malfunction. In order to protect the rail and injectors, the pressure relief valve must be in hydraulic communication with the rail, i.e., in parallel with the pump flow. Two such executions are described in U.S. Pat. Nos. 7,401,593 and 8,132,558.
The executions described in the prior art are successful in their ability to achieve a reasonable relief pressure by hydraulically disabling the relief device during the pumping event when normal high pressure line pulsations occur. However, in high output pump applications there are some significant limitations. Firstly, the necessary increased flow rate and required upsizing of the relief valve device becomes prohibitive in packaging within a modern single piston pump. Secondly, the added flow rate into the low pressure side of the pump by the upsized relief valve device can cause significantly increased low pressure pulsations, leading to failure of the low pressure side components.